1. Field of the Invention
The present invention relates to a method of manufacturing dynamic random access memory (DRAM). More particularly, the present invention relates to a method of manufacturing the double recess crown-shaped capacitor of a DRAM unit.
2. Description of the Related Art
A capacitor is the `heart` of each dynamic random access memory (DRAM) unit. Data in each DRAM unit is stored as charges inside the capacitor. Hence, the larger the capacity for storing electric charges inside a capacitor, the smaller will be the number of soft errors resulting from external interference such as impinging alpha particles. In addition, a capacitor with a large charge storage capacity can lower the refreshing frequency.
Since the capacitance of a capacitor depends on the surface area of the device, how to maintain sufficient capacitance for conducting normal functions when semiconductor device line width is smaller than 0.25 .mu.m has become a major problem. One method of increasing the capacitance of a capacitor is to increase its surface area. For a double-recess crown-shaped capacitor, the method of increasing capacitance is to grow a hemispherical silicon grain (HSG) layer on its interior surfaces. Capacitance is increased due to the extra surface provided by the HSG layer.
In general, a double-recess crown-shaped capacitor is formed by first etching a double-recess crown-shaped trench in a silicon oxide layer. A doped polysilicon layer conformal to the surface profile is next formed over the interior surface of the trench and the silicon oxide layer. Hemispherical silicon grain (HSG) is grown on the surface of the doped polysilicon layer. Photoresist is deposited into the trench and over the doped polysilicon layer so that the hemispherical silicon grains on the doped polysilicon layer are protected by a photoresist layer. The photoresist and doped polysilicon to above the silicon oxide layer are remove by etching or chemical-mechanical polishing (CMP) so that neighboring capacitors are isolated. Finally, the photoresist layer and the silicon oxide layer are sequentially removed to form the lower electrode of the double-recess crown-shaped capacitor.
In the aforementioned method of forming the double recess crown-shaped capacitor, the photoresist layer and the silicon oxide layer must be removed using two different processes, thereby increasing processing complexity. Furthermore, if chemical-mechanical polishing is carried out to form the necessary isolation between different capacitors, special equipment must be installed because worn off photoresist particles may adhere to the polishing pad of the chemical-mechanical polishing station, thereby affecting the polishing action.